A controlled experiment which simulated the standard reporting practices used by radiologists was
performed on IRIS to (1) assess the quality of reporting using digital images and (2) evaluate the use of
enhancement tools. Reports generated by 5 experienced radiologists using IRIS were compared to
reports generated by the same radiologists using analog films on the same emergency department
cases at least seven months earlier. In 100 cases, nine findings were missed using IRIS and 14 new
findings were identified using IRIS. To make diagnoses, enhancements which caused the image to be
darker and increased contrast were most frequently used. There was no systematic relationship
between the enhancement tools used and different types of cases.

We have developed a practical digital imaging colposcope for use in research on early detection of cancerous and
pre-cancerous tissue in the cervix. Several copies of the system have now been used in a variety of clinical and research
environments. Two issues of considerable interest which emerged early in our work involved the roles of color and spatial
resolution as they applied to digital imaging colposcopy. In each instance these qualities potentially have a significant
impact on the diagnostic efficacy of the system. In order to evaluate the role of these parameters we devised and conducted
a receiver operating characteristic (ROC) evaluation of the system. It is apparent from these tests that a spatial resolution
of 512 x 480 pixel with 7 or 8 bits of contrast is adequate for the task. The more interesting result arises from the study of
the use of color in these examinations; it appears that in general, contrary to the widely held perception of the physicians
involved, color apparently provides the clinician with little or no diagnostic information. Indeed, in some instances, access
to color seemed to confuse the physician and resulted in an elevated rate of false positives. Results of the ROC tests are
presented in this paper along with their implications for further development of this imaging modality.

Computed radiography uses a photostimulable phosphor coated imaging plate which is
exposed to x-rays and laser read to form an image. After laser reading, there is a
considerable amount of energy remaining on the imaging plate which is not used. This study
simulated a change in the laser readout process to utilize more of the energy on the image
plate, and potentially improve image quality without changing exposure factors. Images of a
contrast detail phantom were made before and after alteration of the readout process and
analyzed by both physical and psychophysical means. It was found that there is an increase
in the signal-to-noise ratio, when measured with an aperture of the size of a single pixel
(linear dimension about 0.15 mm). However there is no change in the signal-to-noise ratio,
when measured with apertures of the size of 0.75 mm (5 x 5 pixels) and 1.5 mm (10 x 10
pixels). This agrees with the results of the contrast detail study: after alteration, the
observers did not detect smaller objects than they had before the alteration. It appears the
imaging plate readout process is fairly optimized.

A major difficulty with currently available display systems is contrast
rendition. The number of gray steps that can be displayed by a digital system
driving an analog display is determined by the luminance range of the display
and the signal-to-noise ratio (Schreiber, 1986). For a good display this might
be 128 steps (7 bits). The minimal detectable contrast is determined by the
average luminance at the eye and the image noise. Pizer and Chan (1979) using
ROC techniques found the "perceived dynamic range" of a "high quality W
monitor" to be about 87 steps. In their experiment, the eye was adapted to each
luminance level. In a display like the chest with large bright and dark areas
(heart and mediastinum vs. lungs) the eye will be adapted to some intermediate
level and not optimally coupled to either the bright or the dark area. For this
reason gray scale image processing is used for matching correctly the display
to the observer' s perceptual system (Kundel, 1986). There have been some
attempts to develop "perceptually relevant" gray scales (Johnston et al.,1985).
Clinicians do not seem willing to spend the time needed to adjust optimally the
controls at a display console. Even when the controls are fairly simple they
still prefer images that technicians have recorded on film using some
prescription for window and level. Perhaps they do not know how to optimize the
contrast in the image and prefer to leave it to someone else or perhaps the
controls are not as simple as they look.
We have been working on a rule-based system that will select the proper gray
scale transfer characteristic (GSTC) for the initial look at the image. It is
based on the notion that there is an optimal GSTC for each diagnostic finding
on the image and that for most images the diagnostic findings can be predicted
from prompts derived directly from the clinical history. If this is the case,
radiologists who receive diagnostic prompts should be able to predict the
appropriate GSTC.
This experiment was done to determine if radiologists can agree about the GSTC
that will optimize the video display for particular diagnoses.

This paper raises methodological questions concerning Free-Response Receiver Operating Characteristic
(FROC) analysis as used to judge the quality of images in radiology. This paper has three purposes: describing
FROC analysis as used in the literature; discussing whether FROC methods achieve their objectives; and
identifying several methodological shortcomings in FROC at the present state of the art that must be solved if
FROC is to be fully useful.

As Picture Archiving and Communication System (PACS) technology has matured, video image capture has become a
common way of capturing digital images from many modalities. While digital interfaces, such as those which use the
ACR/NEMA standard, will become more common in the future, and are preferred because of the accuracy of image
transfer, video image capture will be the dominant method in the short term, and may continue to be used for some time
because of the low cost and high speed often associated with such devices. Currently, virtually all installed systems use
methods of digitizing the video signal that is produced for display on the scanner viewing console itself.
A series of digital test images have been developed for display on either a GE CT9800 or a GE Signa MRI scanner. These
images have been captured with each of five commercially available image capture systems, and the resultant images
digitally transferred on floppy disk to a PC1286 computer containing Optimast' image analysis software. Here the images
can be displayed in a comparative manner for visual evaluation, in addition to being analyzed statistically. Each of the
images have been designed to support certain tests, including noise, accuracy, linearity, gray scale range, stability, slew
rate, and pixel alignment. These image capture systems vary widely in these characteristics, in addition to the presence or
absence of other artifacts, such as shading and moire pattern. Other accessories such as video distribution amplifiers and
noise filters can also add or modify artifacts seen in the captured images, often giving unusual results.
Each image is described, together with the tests which were performed using them. One image contains alternating black
and white lines, each one pixel wide, after equilibration strips ten pixels wide. While some systems have a slew rate fast
enough to track this correctly, others blur it to an average shade of gray, and do not resolve the lines, or give horizontal or
vertical streaking. While many of these results are significant from an engineering standpoint alone, there are clinical
implications and some anatomy or pathology may not be visualized if an image capture system is used improperly.

The affects of quantization noise in magnetic resonance images (MRI) were studied, and simple modifications are
shown to give significant improvement in subjective image quality and in some quantitative measurements. A liver
phantom based on a MR liver image was created to simulate the effects of quantizing the MR signal. The MR signal
which would be generated by this phantom was characterized and used to study quantization effects as well as to
help in developing a more efficient quantization scheme.
Uniform quantization of the signal was simulated to determine the effects of quantization noise on the liver
phantom. Quantitative measurements using SNR and detectability were made and used as a basis of comparison
for similar measurements utilizing other quantizers including uniform quantization with quantizer overload and
logarithmic quantization. Quantitative measurements were again made and compared to the full range uniform
quantizer. Simulations were performed without additive noise, and results are given in the form of graphs, tables,
and actual images. Simulations were also performed with noisy data but are not reported in detail in this paper.
Q uantitative measurements were consistent in most cases and agreed well with subjective evaluations.
It was found that uniform quantization noise can significantly affect image quality. It was also determined, by
using a logarithmic quantizer or by simple overloading of the uniform quantizer, that significant improvements in
image quality can be achieved. The results are extensible to other image collection systems, particularly those with
high dynamic range.

Digital film scanning/printing systems which do not alter the diagnostic content of radiographs are required for
diagnostic teleradiography, electronic image archiving, and image enhancement. Described is a high fidelity system
capable of digitizing and reprinting films with minimal alteration of detail or degradation of noise for either general
radiographs or mammograms. The system transfers resolution up to 10 lp/mm and has a useful density range of 0-3.5.
Examples of chest, bone and breast films are presented.

Proc. SPIE 1232, Comparison of the physical performance of high-resolution CRT displays and films recorded by laser image printers and displayed on light-boxes and the need for a display standard, 0000 (1 July 1990); doi: 10.1117/12.18846

Performance figures are reported on absolute luminance, luminance uniformity, characteristic display function,
internal scatter, dynamic range, distortion, modulation transfer and its spatial uniformity, and temporal and spatial
noise of two commercial ORT display systems as well as films printed by laser image recorders and displayed on
light-boxes. One of the ORT displays has a matrix of nominally 2000 x 2000 pixels, the other of 1000 x 1500 pixels.
The laser image recorders cover a matrix of 3500 x 2200 pixels.
When comparing equal pixel matrices of hard versus soft copy displays, typically hard copies facilitate greater
information transfer than soft copies due to a presentation with higher absolute luminance, greater perceived
dyiiainic range, and better spatial resolution. Perceived dynamic range and resolution are partially degraded in
the ORT displays by internal scatter. Soft and hard copy displays are about equivalent in terms of luminance
non-uniformity, noise, and geometrical distortion. All displays differ in their characteristic display functions and
thus in perceived contrast resolution.
A display function standard is proposed to the industry by which mismatches between hard and soft copy
presentations can be nimized as well as means for maintaining standardized performance.

This paper describes the results of measurements which permit determination of the
maximum information content of images displayed with a high resolution CRT of a nominal
pixel matrix of 2000 x 2000 adressable pixels. These measurements are based on the precise
determination of signal, noise and spatial resolution. Noise is measured both as temporal noise
and as spatial noise, using both temporal and spatial sampling techniques.
The dynamic range as given by the maximum and minimum values of luminance can be
as high as 1900, however for practical settings of brightness and contrast it is about 424.
The dynamic range is reduced from 424 to 1 38 as a result of veiling glare when the SMPTE
pattern is displayed.
The spatial noise was significantly larger than the temporal noise: For a command level
of GL = 255, a single pixel and a single CRT frame, the temporal signal-to-noise Eatio was
59, while the spatial signal-to-noise ratio was only 7. The RMS noise (both spatial and
temporal) was proportional to the squareroot of the respective bandwidths. Both temporal and
spatial noise power spectra were independent of their respective frequencies (white noises).
In the average, the size of a pixel was much larger than the size of an addressable
pixel, indicating, that the total number of usable pixels was smaller than the number of
addressable pixels: Instead of the addressable pixelmatrix of 2000 x 2000 pixels, we estimated
only 532 x 548 "Noise-Equivalent" pixels.
It was estimated, that for spatial integration over a single pixel and temporal
integration over a single CRT frame, the maximum information content of images produced by
this monitor, is 1.72 x 106 bits, based on temporal noise; however due to spatial noise that
number is reduced to 1.28 x 106 bits. This contrasts sharply with the nominal information
content of 3.2 x 107 bits as determined from the nominal raster of 2000 x 2000 pixels and
the 8 bits digitization at the display buffer.

Two methods of image display are developed in which the best 5-7 images of the peripheral arteries are joined together to form a single, continuous image of the legs. First, a complete image of both legs, called WHOLE LEG, is reduced so that it fits on a single monitor or hardcopy image. Second, a full resolution image, called SCROLL, is assembled that can be scrolled on a video monitor. From the geometrical parameters of the acquisition (source-to_detector distance, table height, etc.), the portions of each image to remove beforejoining the remaining portions together are estimated. This estimate is refined using an automatic search for the best match. To correct for body taper, images are intensity equalized. Using a reconstruction method that assumes a planar geometry results in a volume that is displayed in neighboring image frames and a volume that is never displayed. Nevertheless, WHOLE-LEG is aesthetically pleasing. In the case of SCROLL, images are displayed such that every part of each input image is displayed at one time or another. A video tape of SCROLL shows how this works.

The work described here is the result of an attempt to implement a unified representation for the display,
storage, model matching, location and analysis of cardiac images. The Symmetrical Axis Tranaform (SAT) has
attributes which make it useful for object representation, induding 3-D objects. It is hierarchical, compact, exact
and fast. Using these characteristics, object recognition has been done using SAT [6], and means of obtaining
surface descriptions for 3-D object8 has been reported [4]. The SAT has been described using morphological
operations [5]. This paper describes an extension of the SAT to the representation of arbitrary non-Eudidean
surfaces using geodesic operators put forth by Lantejoul and Beucher [2].

Transparent Volume Imaging began with the stereo xray in 1895 and ended for most
investigators when radiation safety concerns eliminated the second view. Today,
similiar images can be generated by the computer without safety hazards providing
improved perception and new means of image quantification.
A volumetric workstation is under development based on an operational prototype. The
workstation consists of multiple symbolic and numeric processors, binocular stereo
color display generator with large image memory and liquid crystal shutter, voice
input and output, a 3D pointer that uses projection lenses so that structures in 3
space can be touched directly, 3D hard copy using vectograph and lenticular printing,
and presentation facilities using stereo 35mm slide and stereo video tape projection.
Volumetric software includes a volume window manager, Mayo Clinic's Analyze program
and our Digital Stereo Microscope (DSM) algorithms. The DSM uses stereo xray-like
projections, rapidly oscillating motion and focal depth cues such that detail can be
studied in the spatial context of the entire set of data. Focal depth cues are
generated with a lens and apeture algorithm that generates a plane of sharp focus,
and multiple stereo pairs each with a different plane of sharp focus are generated
and stored in the large memory for interactive selection using a physical or symbolic
depth selector. More recent work is studying non-linear focussing.
Psychophysical studies are underway to understand how people perce ive images on a
volumetric display and how accurately 3 dimensional structures can be quantitated
from these displays.

We have developed the algorithm and the computer program
that constructs three dimensional image (3D) of soft tissue from
multiple 2D slices of computed tomograph(CT) and magnetic
resonance(MR) images. In construction of MR-3D, we have used
multi-spin-echo images, and performed segmentation by comparing
the curve-shape(intensity vs number of echo) of each pixel with a
standard curve-shape that belongs to the desired organ. In the segmentation
for CT-3D, we have used two kinds of threshold. In
addition to CT value, we have used differential intensity of image
as the threshold. The 3D micro-program has been installed in the
Image Workstation of PACS. The position of observer's eye can be
changed in less than a few seconds.

SOFTVU is a collection of computer programs capable of performing several image manipulation tasks required
to visualize and analyze multidimensional image data obtained from medical imaging scanners. In this paper we
present some novel image segmentation, interpolation, and display techniques developed and implemented in the
package. Our rule-based segmentation can automatically extract different structures of the brain from MR image
data. The shape-based interpolation scheme presented here minimizes user involvement in interactive segmentation
and enhances portrayal of dynamic as well as static objects. The rendering subsystem can render multiple objects
with color and cut-away sections. The system as a whole provides efficient software solutions to several clinical
image analysis tasks.

We present two methods for acquiring and viewing integrated 3-D images of cerebral vasculature and
cortical anatomy. The aim of each technique is to provide the neurosurgeon or radiologist with a 3-D
image containing information which cannot ordinarily be obtained from a single imaging modality. The
first approach employs recent developments in MR which is now capable of imaging flowing blood as well as
static tissue. Here, true 3-D data are acquired and displayed using volume or surface rendering techniques.
The second approach is based on the integration of x-ray projection angiograms and tomographic image
data, allowing a composite image of anatomy and vasculature to be viewed in 3-D. This is accomplished by
superimposing an angiographic stereo-pair onto volume rendered images of either CT or MR data created
from matched viewing geometries. The two approaches are outlined and compared. Results are presented
for each technique and potential clinical applications discussed.

Stereolithography, a new technique of prototype fabrication developed for the aerospace industry, offers
a unique way to display patient anatomy. Like current computer-aided-design (CAD) systems, it uses
digital image data from CT and MR to produce a physical model. Unlike conventional CAD it does not
require a cutting tool and therefore CAD tool-path limitations do not exist. The stereolithography
apparatus (SLA) uses an ultraviolet laser to selectively polymerize and solidify a polymeric liquid
plastic solution under computer control. The device was used to produce a model of cranial bony
anatomy from CT image data providing full internal detail in the constructed model including encased
sinuses, foramen, and potentially complete internal anatomy within a closed skull. The advantages and
disadvantages of this technology are reviewed with an emphasis on future development.

The aim of this application is to interactively transfer information between CT, MRI or DSA data and a 3D stereotactic
atlas digitized on a C. Based on a 3D organization of data, this system is devoted to assist a neurosurgeon in surgical
planning by numerically cross-assigning information between heterogeneous data (in-vivo or atlas). All these images can be
retrieved in digital form from the PACS central archive (SIRENE PACS system).
The basic feature of this confrontation is the Talairach's proportional squaring which consists in dividing the 3D cerebral
space in independently deformable sub-parts. This 3D model is based on anatomical structures such as the AC-PC line and
its two associated vertical lines VAC and VPC. Based on this proportional squaring, the atlas has been digitized in order to
get atlas plates along the three orthogonal directions of this geometrical reference (axial, coronal, sagittal).
The registration of in-vivo data to the proportional squaring is done by extracting either external framework landmarks or
anatomical reference structures (i.e. AC and PC structures on the MRI sagittal mid-plane image). Geometrical
transformations and scaling are then recorded for each modality or acquisition according to the proportional squaring. These
transformations make for instance possible the transfer of a 3D point of a MRI examination to its 3D location within the
proportional squaring and furthermore to its 3D location within another data set (in-vivo or atlas). From that stage, the
application gives the choice to the neurosurgeon to select any confrontation between input data (in-vivo images or atlas) and
output data (id).

With the integration of computer graphics to presently available computed tomography, magnetic resonance
imaging, and positron emission tomography scan devices, processing and displaying three dimensional data arrays is
rapidly becoming important. Present systems can model full color, complex two or three dimensional objects, and
manipulate their perspective displayed appearance in real time. However, even with the many hardware and software
tools available for providing enhanced versions of two or three dimensional information,the rapid developments within
these areas continues to outpace the ability of users to learn and use them efficiently. At the University of Tennessee
Space Institute, Department of Electrical Engineering, and Vanderbilt University Medical Center, Department of
Radiological Sciences, research is being performed to develop a voice actuated computer graphics system that responds
interactively with the human voice. The research uses a Texas Instruments voice recognition and speech synthesis
board, a Texas Instruments 955 computer workstation, and a Sun Microsystems 4/280 color graphics workstation.
Verbal commands are used to control the graphics system programs, set parameters for displaying two and three
dimensional views, and instruct the system for additional cross-sections, viewing references, display formats, etc.
Verbal responses from the computer inform the user when additional information is needed or error conditions have
occurred. The system provides a means for users to conduct an interactive verbal dialogue with the computer for
rendering and displaying complex medical imaging data.

A cost-effective personal workstation has been designed and developed using PC
based commercial products, to assist physicians and scientists who are interested in
creating teaching programs based on CT and MR images, collecting interesting cases,
carrying out research projects requiring original digital image information, or
generating reports. The development hardware is based on an IBM PS/2 Model 80
with a 85 14 graphics adaptor, an optical disk, a trackball, a digitizing pad, a 9 track
tape drive, a mouse, a T800 transputer card, an Ethernet card, a voice recognition
card, and a fax machine. The software development has been done using Microsoft
C under Windows/286, such that software can be used with any 80286/80386 PCs
capably of supporting Windows/286.

During a clinical trial, emergency physicians and radiologists at the Ottawa Civic Hospital used
IRIS (Integrated Radiological Information System) to process patients' x-rays, requisitions, and
reports, and to have consultations, for 319 active cases. This paper discusses IRIS user interface issues
raised during the clinical trial.
The IRIS workstation consists of three major system components: 1) an image screen for viewing
and enhancing images; 2) a control screen for presenting patient information, selecting images, and
executing commands; and 3) a hands-free telephone for reporting activities and consultations. The
control screen and hands-free telephone user interface allow physicians to navigate through patient
files, select images and access reports, enter new reports, and perform remote consultations.
Physicians were observed using the system during the trial and responded to questions about the user
interface on an extensive debriefing interview after the trial.
Overall, radiologists and emergency physicians were satisfied with IRIS control screen
functionality and user interface. In a number of areas radiologists and emergency physicians
differed in their user interface needs. Some features were found to be acceptable to one group of
physicians but required modification to meet the needs of the other physician group. The data from the
interviews, along with the comments from radiologists and emergency physicians provided important
information for the revision of some features, and for the evolution of new features.

In this document we describe the design of FilmPlane2, its user interface and implementation. The
underlying mental model of the workstation design is that of a virtual electronic view box. Viewed
"from a distance" the whole view box can be seen, but with only in rough detail. Viewed "from up
close", individual images can be seen at full resolution. The system provides a natural way to determine
which images show up in the "up close" view. Additional features allow for sequential and nonsequential
access to images, measuring anatomical features, contrast adjustment, and limited zooming.
FilmPlane2 is being implemented using X Windows and C++. The full system is designed to run on a
Stellar graphics workstation with three 1280x1024 greyscale display screens, as well as Sun and DEC
workstations. The system can be adapted to an arbitrary number of display screens.

A distributed CT/MR digital viewing station for the neuroradiology section has been developed and is being evaluated in our department. The major components of the station consist of a SUN host computer, a PIXAR II image processor, and four 1K x 1K progressive video monitors. The software modules operating in the station include an image acquisition process, a local database process, and an user image display and processing process. Functions provided by the station are described. Preliminary results obtained from clinical evaluation are reported. Future plans to refine the station are presented.

The Multi-modality Image Display Station (MIDS) is designed for the use of physicians outside
of the radiology department. Connected to a local area network or a host computer, it
provides speedy access to digitized radiology images and written diagnostics needed by attending
and consulting physicians near the patient bedside. Emphasis has been placed on low
cost, high performance and ease of use. The work is being done as a joint study with the
University of Texas Southwestern Medical Center at Dallas, and as part of a joint development
effort with the Mayo Clinic. MIDS is a prototype, and should not be assumed to be an
IBM product.

Biomedical structures such as the beating heart are inherently multi-dimensional in nature. In addition
to the three spatial directions which represent the object location and orientation, higher order
dimensions can be assigned to represent various object parameters such as time and tissue density. In
this paper, we propose a hierarchical data structure which can be mapped into a computer architecture
that will efficiently store, manipulate, and display time varying images of multi-dimensional biomedical
structures. This n-D object representation scheme which is called a linear hypertree is a generalization
of the linear quadtree and octree from their respective 2-D and 3-D spaces to n-D environment. It is
a hierarchical data structure which represents multi-dimensional volumetric information in a 2'-way
branching tree. The basic properties of a linear hypertree are briefly presented along with the procedure
for encoding the node rectangular coordinates into a hierarchical locational code. Two decoding techniques
that transform the node locational code into its rectangular coordinate format are introduced.
Some adjacency concepts in a multi-dimensional environment are defined. A neighbor finding algorithm
which identifies the locational code of the adjacent hypertree node in a given direction is also presented.
This algorithm does not convert the locational code to its rectangular coordinate form; instead, it operates
directly on the node locational code in order to determine the neighbor's identification. Finally,
Procedures for computing the locational codes of larger and smaller size neighbors are also included.

A new method for spatial-frequency analysis, the Frazier-Javierth transform (FJT), has recently been introduced
which allows the simultaneous encoding of image properties in both the space and frequency domains.
This technique appears to have applicability to the problem of image data compression, in a way similar to the
Fourier transform or discrete cosine transform. A necessary step in the development of an FJT compression
algorithm is to produce a method for appropriately quantizing the FiT coefficients.
The current work undertakes the measurement of the thresholds for the visual detection of the FJT basis
functions. These results will be used in the development of a psychovisually-based quantizer. The thresholds
were determined by the use of psychovisual observer experiments. It is shown that the detectability of the basis
functions is in accord with current knowledge of the spatial frequency sensitivity of the human visual system.
However, these results are not predictable from simple psychovisual models, and because of the frequency domain
behavior of the FJT, the measured values must be corrected before they can be used in a quantizer. The corrected
values imply that the FJT quantizer may not match the properties of ordinary images as well as the psychovisual
quantizers used for such methods as the discrete cosine transform.

The ACR-NEMA Standard was published five years ago. Implementations are just now becoming available in a form
other than a prototype. Though this seems like a long interval between the initial work and results, the organization
responsible for the Standard, the ACR-NEMA Digital Imaging and Communications Standards Committee, has not been
idle. Much of the progress which has been made is the result of cooperative work involving industry, the Committee and its
Working Groups (WG), and the medical imaging user community.
This paper will briefly review the history of the development of what is now a family of ACR-NEMA standards,
describe the current activity of the Working Groups, and indicate in what directions the WGs are headed for both new and
updated standards.

A compression scheme is described that allows high-definition radiological images with greater than 8-bit intensity
resolution to be represented by 8-bit pixels. Reconstruction of the images with their original intensity resolution
can be carried out by means of a pipeline architecture suitable for compact, high-speed implementation. A
reconstruction system is described that can be fabricated according to this approach and placed between an
8-bit display buffer and the display's video system thereby allowing contrast control of images at video rates.
Results for 50 CR chest images are described showing that error-free reconstruction of the original 10-bit CR
images can be achieved.

A new decomposition method using image splitting and gray-level remapping has been proposed for
image compression, particularly for images with high contrast resolution. The effects of this method are
especially evident in our radiological image compression study. In our experiments, we tested the
impact of this decomposition method on image compression by employing it with two coding techniques
on a set of clinically used CT images and several laser film digitized chest radiographs. One of the
compression techniques used was full-frame bit-allocation in the discrete cosine transform domain,
which has been proven to be an effective technique for radiological image compression. The other
compression technique used was vector quantization with pruned tree-structured encoding, which
through recent research has also been found to produce a low mean-square-error and a high
compression ratio. The parameters we used in this study were mean-square-error and the bit rate
required for the compressed file. In addition to these parameters, the difference between the original and
reconstructed images will be presented so that the specific artifacts generated by both techniques can be
discerned by visual perception.

Transform based compression methods achieve their effect by taking advantage of the correlations
between adjacent pLtels in an image. The increasing use of three-dimensional imaging studies in
radiology requires new techniques for image compression. For time-sequenced studies such as digital
subtraction angiography, pixels are correlated between images, as well as within an image. By using
three-dimensional cosine transforms, correlations in time as well as space can be exploited for image
compression. Sequences of up to eight 512 x 512 x 8-bit images were compressed using a single full volume
three-dimensional cosine transform, followed by quantization and bit-allocation. The
quantization process is a uniform thresholding type and an adaptive three-dimensional bit-allocation
table is used. The resultant image fidelity vs. compression ratio was shown to be superior to that
achieved by compressing each image individually.

In this paper, we report on an experiment in which various lossy image coding techniques are applied to
a digitized radiographic image. The coding schemes are applied to radiograph, digitized using the Konica
laser based scanner. Six different lossy coding techniques are employed as follows: full frame transforms,
variable length block transform coding, three vector quantization schemes which differ in the degree of
adaptivity, and a unified variable length transform coding and adaptive vector quantization. The first
vector quantizer uses an universal code book which has been designed from a large set of radiographs;
whereas, the second vector quantizer uses a reduced set of code words drawn from the universal codebook.
The use of smaller set of code words effectively means that less bits are needed for specifying the
codeword label and so decreasing the bit rate requirements. In the last vector quantizer, a new codebook
is designed for each image, so decreasing the bit rate required for the label, but increasing the overhead
required for transmitting the new code book. The unified variable length transform coding and adaptive
vector quantization technique involves variable length transform coding on the code book of the last
vector quantizer, thus reducing the overhead for code book transmission.

Color 35mm photographic slides are commonly used in
dermatology for education, and patient records. An electronic
storage and retrieval system for digitized slide images may offer
some advantages such as preservation and random access. We have
integrated a system based on a personal computer (PC) for digital
imaging of 35mm slides that depict dermatologic conditions. Such
systems require significant resources to accommodate the large
image files involved. Methods to reduce storage requirements and
access time through image compression are therefore of interest.
This paper contains an evaluation of one such compression method
that uses the Hadamard transform implemented on a PC-resident
graphics processor. Image quality is assessed by determining the
effect of compression on the performance of an image feature
recognition task.

Both CT and MRI images present three-dimensional information
as a series of two-dimensional slices. In conventional film
sheet display, recovering the third dimension of information
requires the physician to mentally reconstruct the volume. This
complex process inhibits the understanding of three dimensional
registration of both lesions and normal structures of surgical
concern.
We have developed a technique for the computerized
generation of a wire-frame model from the raster image set. By
using a 10242 pixel display, any three raster frames plus the
wire-frame may be simultaneously displayed. Each raster frames's
location is displayed on the wire-frame providing perspective
clues as to the three-dimensional relationship between frames.
Each raster image may be changed with real time tracking on the
wire-frame model. The wire-frame may be formed from either CT or
MRI images and takes less than two minutes for a standard 25
slice head series.

This paper addresses the issue of increasing productivity in experimenting with and using image analysis algorithms.
Algorithm developers typically experiment with new algorithms in an environment consisting of an editor and
compiler on general purpose computers. Such an environment has several disadvantages: (i) It is non-interactive in
that the experimenter must go through several steps (e.g. editing, compiling and linking) to see the result of his
changes; (ii) It forces the experimenter to concentrate on the details of the compiler instead of the details of the
algorithm; (iii) The software so produced frequently demonstrates techniques of programming expediency instead of
techniques which lend themselves to parallel implementation. These disadvantages stifle creativity and reduce
productivity.

A teaching station for MR technologists based on a personal computer system has
been designed and developed. The system is designed mainly to train technologists,
who have experiences with other imaging modalities like CT, ultrasound, or nuclear
medicine.

The application of digital technologies to chest radiography holds
the promise of routine application of intage processing techniques to
effect image enhancement. However, due to their inherent spatial
resolution, digital chest images impose severe constraints on data
storage devices. Compression of these images will relax such
constraints and facilitate image transmission on a digital network.
We have evaluated image processing algorithms aimed at compression
of digital chest images while improving the diagnostic quality of the
image. The image quality has been measured with respect to the task
of tumor detection. Compression ratios of as high as 2:1 have been
achieved. This compression can then be supplemented by irreversible
methods.

Progressive image transmission is receiving attention for application in interactive image communication over low-bandwidth channels. In progressive image transmission, a low-resolution
image is first transmitted. Upon the user's request, the low-resolution image can be then refined
progressively with further transmission until the original image is losslessly reproduced.
One important class of encoding for progressive image transmission is based upon pyramid data
structures where the intermediate levels correspond to reduced-resolution approximations. Progressive
image transmission is achieved by sending the data stored in the pyramid starting from
the top level. In this paper, we present a comparison of various pyramid data structures for
progressive transmission of medical imagery. These pyramid data structures include the mean,
reduced-sum, difference, reduced-difference, S-transform and Gaussian-Laplacian pyramids. The
simulations are carried out on a set of digitized radiographic images. The simulation results
demonstrate that the reduced-difference pyramid achieves the best performance in terms of three
criteria: the equivalent entropy, rate distortion performance and total lossless transmission hit
rate. Furthermore, the quality of the intermediate level images is seen to be improved by using
an appropriate interpolation function.

Vector quantization has been widely used in image encoding systems and speech recognition systems
science 1980's. In this paper, three kinds of vector quantization approaches are introduced, which are based
on neural networks. The principles of using neural networks to improve the performance of vector quantization
are described. Because of high parallel computation, learning function, high fault tolerance and selforganizing
capability of neural networks, the performance of vector quantizers is improved.

The use of coherent fiber-optic bundles as image conduits has increased significantly
in recent years. Fiber bundles permit optical inspection of small, previously inaccessible
places. Applications in industrial vision, medicine, aerospace instrumentation and other
areas are developing rapidly. The resolution of the image transmitted by fiber bundles is
primarily limited by the diameter of the individual fibers. The image is further distorted
by a number of factors such as the wide and occasionally skewed point spread function of
each fiber and the non-uniformity of fiber characteristics throughout the bundle.
Additionally, the appearance of the characteristic circular or hexagonal fiber walls is
distracting and objectionable to viewers and increases the complexity of machine vision
algorithms. We report a sequence of image processing steps on digitized coherent bundle
images which results in complete removal of the fiber wall patterns from the transmitted
images; along with corrections for factors creating distortion. The processing steps
essentially involve 1) calibrating the fiber bundle under uniform illumination, 2) locating
the center of each fiber and extracting the centroid value, 3) disseminating the centroid
values onto a uniform grid, and 4) reconstructing the complete image by interpolating
between nearest neighbor points on the uniform grid. The process has been applied to
both monochrome and color images by applying the above steps individually to each of
the red, green and blue components. Future work needs to be performed to correct for a
visible moire pattern and the inherent smoothing caused by the interpolation process.

The medical imaging field relies increasingly on imaging and graphics techniques in diverse applications with needs similar to
(or more stringent than) those of the military, industrial and scientific communities. However, most image processing and
graphics systems available for use in medical imaging today are either expensive, specialized, or in most cases both. High
performance imaging and graphics workstations which can provide real-time results for a number of applications, while
maintaining affordability and flexibility, can facilitate the application of digital image computing techniques in many different
areas.
This paper describes the hardware and software architecture of a medium-cost floating-point image processing and display
subsystem for the NeXT computer, and its applications as a medical imaging workstation. Medical imaging applications of
the workstation include use in a Picture Archiving and Communications System (PACS), in multimodal image processing
and 3-D graphics workstation for a broad range of imaging modalities, and as an electronic alternator utilizing its multiple
monitor display capability and large and fast frame buffer.
The subsystem provides a 2048 x 2048 x 32-bit frame buffer (16 Mbytes of image storage) and supports both 8-bit gray scale
and 32-bit true color images. When used to display 8-bit gray scale images, up to four different 256-color palettes may be
used for each of four 2K x 2K x 8-bit image frames. Three of these image frames can be used simultaneously to provide pixel
selectable region of interest display. A 1280 x 1024 pixel screen with 1: 1 aspect ratio can be windowed into the frame buffer
for display of any portion of the processed image or images. In addition, the system provides hardware support for integer
zoom and an 82-color cursor. This subsystem is implemented on an add-in board occupying a single slot in the NeXT
computer. Up to three boards may be added to the NeXT for multiple display capability (e.g., three 1280 x 1024 monitors,
each with a 16-Mbyte frame buffer).
Each add-in board provides an expansion connector to which an optional image computing coprocessor board may be added.
Each coprocessor board supports up to four processors for a peak performance of 160 MFLOPS. The coprocessors can
execute programs from external high-speed microcode memory as well as built-in internal microcode routines. The internal
microcode routines provide support for 2-D and 3-D graphics operations, matrix and vector arithmetic, and image processing
in integer, IEEE single-precision floating point, or IEEE double-precision floating point.
In addition to providing a library of C functions which links the NeXT computer to the add-in board and supports its various
operational modes, algorithms and medical imaging application programs are being developed and implemented for image
display and enhancement. As an extension to the built-in algorithms of the coprocessors, 2-D Fast Fourier Transform (FF1),
2-D Inverse FFF, convolution, warping and other algorithms (e.g., Discrete Cosine Transform) which exploit the parallel
architecture of the coprocessor board are being implemented.

A receiver operating characteristic (ROC) experiment is used to compare the diagnostic
performance of analog film to digital hardcopy and compressed hardcopy. The
compression is done using a full-frame bit-allocation algorithm carried through on a
custom designed board residing on a SUN computer bus. Image set included thirthy-one
radiographs with septal lines (n=18) and/or parenchymal nodules (n=14), with six
radiographs that had neither abnormality. Six radiologists viewed the image set under
each modality. There is no statistically significant difference between the three
modalities.

Signal processing concepts are used to study the problems of obtaining continuous image
representations in terms of B-spline basis functions, and performing reconstructions at various
magnifications. Filters that compute direct or indirect B-spline transformations are derived and
characterized in terms of their z-transforms for polynomial splines of any order. Efficient recursive
implementations of these operators are proposed. Recursive filters that efficiently solve the problem of
approximating a signal through the use of least squares splines are also derived. This last procedure is
analogous to the application of an anti-aliasing filter prior to decimation for the representation of a signal
with fewer samples.

Image compression at rates of 10:1 or greater could make PACS much more responsive and economically attractive. This
paper describes a protocol for subjective and objective evaluation of the fidelity of compressed/decompressed images to the
originals and presents the results ofits application to four representative and promising compression methods. The methods
examined are predictive pruned tree-structured vector quantization, fractal compression, the discrete cosine transform with equal
weighting of block bit allocation, and the discrete cosine transform with human visual system weighting of block bit
allocation.
Vector quantization is theoretically capable of producing the best compressed images, but has proven to be difficult to
effectively implement. It has the advantage that it can reconstruct images quickly through a simple lookup table.
Disadvantages are that codebook training is required, the method is computationally intensive, and achieving the optimum
performance would require prohibitively long vector dimensions. Fractal compression is a relatively new compression
technique, but has produced satisfactory results while being computationally simple. It is fast at both image compression and
image reconstruction. Discrete cosine iransform techniques reproduce images well, but have traditionally been hampered by
the need for intensive computing to compress and decompress images.
A protocol was developed for side-by-side observer comparison of reconstructed images with originals. Three 1024 X 1024
CR (Computed Radiography) images and two 512 X 512 X-ray CT images were viewed at six bit rates (0.2, 0.4, 0.6, 0.9,
1.2, and 1.5 bpp for CR, and 1.0, 1.3, 1.6, 1.9, 2.2, 2.5 bpp for X-ray CT) by nine radiologists at the University of
Washington Medical Center. The CR images were viewed on a Pixar II Megascan (2560 X 2048) monitor and the CT images
on a Sony (1280 X 1024) monitor.
The radiologists' subjective evaluations of image fidelity were compared to calculations of mean square error (MSE),
normalized mean square error (NMSE), percentage mean square error (PMSE), and fractal normalized mean square error
(FMSE) for each compression method and bit rate.

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Advanced PhotonicsJournal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews